The present invention relates to a combustion chamber and process for use in gas turbines.
Combustion chambers for gas turbines are known in which the fuel is injected directly at the upstream end of the flame tube. With these combustion chambers the mixture is not satisfactorily conditioned on account of, chiefly, insufficient atomization of the fuel, of poor mixing with the combustion air, and of insufficient heating of the fuel. Inadequate atomization of the fuel causes relatively heavy emission of injurious matter and environmental contamination. Also, the turbine inlet temperature profiles of these combustion chambers are exceedingly inconsistent and thus detrimental to the useful life of the blades. With again other, known combustion chambers, vaporizer tubes are used in lieu of direct injection. While these vaporizer tubes provide more perfectly conditioned mixtures than will direct injection, they still fail to give entire satisfaction owing to their more narrowly restricted operating range and the low temperatures that these vaporizer tubes will be able to sustain because they are made of nickel alloy.
Practically all known combustion chambers have in common flame tubes generally made of sheet, where use is made of certain nickel alloys as a material. Inasmuch as these materials will not safely sustain temperatures of more than 1300.degree.K, with combustion temperatures running far above, these flame tubes need intensive cooling to prevent their destruction and achieve the long useful life essential to economical operation. However, low wall temperatures resulting from such intensive cooling greatly promotes the formation of soot, which often settles on the cool walls near the nozzle where it impairs the combustion efficiency and frequently occasions malfunctions.
A broad aspect of the present invention is to provide a combustion chamber which, while economizing the cost of manufacture, improves combustion, reduces the emission of injurious matter and promotes favorable turbine inlet temperatures profiles by, particularly, raising the ceiling on wall temperatures and improving the fuel conditioning process.
It is a particular object of the present invention to provide a combustion chamber in which the fuel is conditioned, and mixed with the primary air needed to sustain combustion, in an entirely permeably walled premix chamber attached to the upstream end of the flame tube, and in which combustion occurs, immediately after the mixture issues from the premix chamber, in a combustion zone beginning directly at the intervening diaphragm. In this mixing chamber, partial vaporization of the fuel provides more perfectly conditioned fuel than could be achieved in the previously known combustion chambers, which in turn improves combustion efficiency, shortens the length of flame and considerably improves the resultant temperature profile over previously known temperature profiles. The reduction in the length of combustion zone will naturally also affect to advantage the over-all length of the combustion chamber.
In a further apsect of the present invention, the premix chamber is made of a porous ceramic sinter material enabling it to safely sustain elevated wall temperatures as high as 2000.degree.C, which will in turn provide still more perfectly conditioned fuel and which, most importantly, will prevent the formation and deposition of soot.
In a further aspect of the present invention the premix chamber consists of two parts of which one is an approximately frustum-shaped head member incorporating an opening for the fuel nozzle and of which the other is a disk-shaped diaphragm through which the combustible mixture enters the combustion zone.
This arrangement considerably simplifies the manufacture of the premix chamber and, more particularly, it prevents the thermal stresses which would otherwise be induced in the ceramic components as a result of the elevated temperatures of the diaphragm. Also very importantly, it considerably economizes the cost of manufacture and permits the materials and porosities to be varied between the two components.
In a still further aspect of the present invention the flame tube downstream of the premix chamber incorporates a stepped flare and exhibits inwardly inclined passageways for secondary air. This enables the supply of secondary air at points in close proximity to the combustion zone, without major pressure losses, and in an approximately axial direction with a radial component.